DNA Studies Suggest Emperor Is Most Ancient of Penguins

By CARL ZIMMER

Published: October 11, 2005

Penguins are some of the most improbable animals on the planet. They have wings and feathers but cannot fly. They are not fish, but they have been recorded as deep as 1,755 feet underwater. And the most improbable is the emperor penguin, which waddles across 70 miles of Antarctic ice to reach its breeding grounds. New research on penguin DNA suggests that the emperor also has the most ancient lineage of living penguins.

Scientists have long recognized a link from penguins to petrels and albatrosses. While albatrosses have more conventional bird bodies, they share subtle traits with penguins, like the arrangement of beak bones. They are generally considered the closest living relatives of penguins.

Penguins' ancestors probably began their evolutionary march while Tyrannosaurus rex walked the earth. In a paper to be published in The Proceedings of the Royal Society of London, Canadian scientists investigated the origin of penguins by studying their genes. They analyzed segments from three genes, comparing their sequence in all 18 species of penguins and in other birds.

Mutations can accumulate in genes at a fairly steady rate, so the variation between the species acted as sort of a molecular clock. The researchers, based at the Royal Ontario Museum, concluded that penguins diverged from the ancestors of petrels and albatrosses about 71 million years ago.

It's possible that the earliest penguins resembled petrels, which have short wings that help them dive as far as 240 feet underwater. Over time, penguins may have become more adapted to diving. ''That required sacrificing flight,'' said Norberto Giannini, a biologist at the American Museum of Natural History.

Ewan Fordyce, a paleontologist at the University of Otago in New Zealand, and his colleagues study the oldest known penguin fossils, dating back 60 million to 62 million years. These proto-penguins were not as adapted to diving as today's. Their wings could still bend at the elbow. ''The joint was starting to become stiff, so the wing was starting to evolve into a hydrofoil,'' Dr. Fordyce said. ''In that sense these very early forms are a sort of intermediate.''

The question of how these early penguins gave rise to the living lineages has proved difficult. Some have suggested that emperors evolved recently, for example, while others say they belong to an ancient lineage. But these studies are based on small amounts of data, so results are ambiguous.

''They couldn't get a good answer,'' said Dr. Sergio Luiz Pereira, a member of the team at the Royal Ontario Museum in Toronto.

With more data, Dr. Pereira and his colleagues were able to draw a clearer evolutionary tree. They found that emperors and king penguins belong to the oldest living lineage, while other species are more recent.

Their results agree for the most part with another study that was based on both penguin genes and anatomy, published this June in the journal Cladistics by Dr. Giannini and Sara Bertelli, also at the American Museum of Natural History.

''You see the same major patterns. The picture is well established, I think,'' Dr. Giannini said.

The Canadian researchers found that the penguin's common ancestor existed 40 million years ago -- more than 30 million years after they think penguins evolved. ''There is a big gap there,'' Dr. Pereira said. He proposed that most of the older fossils of penguins (some more than five feet tall) belonged to extinct branches of the tree.

The study also finds that the living species that belong to the oldest branches of the penguin tree -- the gentoo, chinstrap and king penguins, along with the emperor penguins -- can all be found around Antarctica. ''The ancestor of the modern penguins were in Antarctica or very close,'' Dr. Pereira said.

But the early penguins probably did not have to survive brutal conditions on Antarctica as they do today. ''Antarctica was covered in forest, much like we see in New Zealand today,'' Dr. Pereira said.

The ice came later, about 35 million years ago. Geologists suspect that the change occurred as a result of South America and Australia's drifting away from Antarctica. The ocean currents began to circle the continent, isolating it. This cooling climate may have killed off the older penguins. Some researchers have speculated that they disappeared because they couldn't compete with whales hunting for the same prey.

Not all the penguins became extinct. ''Basically, what happened is penguins had to adapt to conditions in Antarctica, or they had to leave,'' Dr. Pereira said. The ancestors of the emperors and other residents of Antarctica evolved the ability to survive the conditions. Other penguins swam north to milder waters, where they founded new lineages. ''Most of the species ended up leaving the continent,'' Dr. Pereira said.

Penguins may have followed ocean currents carrying cool, nutrient-rich waters northward. They established breeding grounds on new volcanic islands and branched off into new species.

The researchers estimate that South American penguins reached the Gal?gos Islands four million years ago, probably following the Humboldt current, which flows along South America. The royal penguin of New Zealand and the macaroni penguin of southern Chile and the Falkland Islands are the youngest species of all, sharing an ancestor that lived only 1.4 million years ago.

Paleontologists welcome the new Canadian study, but they believe it needs to be tested against the fossil record. ''That's got to be the next step,'' said Julia Clarke, a paleontologist at North Carolina State University.

Dr. Fordyce is skeptical about the proposed evolutionary timing, pointing out that the oldest fossils that may belong to living lineages of penguins are only 20 million years old. If the DNA-based study is correct, then half the fossil record is yet to be discovered. ''It's possible that these modern penguins may be hiding somewhere in the fossil record, but I'd be surprised,'' he said..

The history of penguins -- partly driven by a cooling climate -- is now running in reverse. Ocean waters are warming, and it's hard for scientists to forecast how that will affect penguins.

Adelie penguins feed on krill that feed on algae that grows on ice. Adelie penguins have decreased by 70 percent over the past 30 years off the Antarctic peninsula, possibly as a result of retreating sea ice. They are being replaced by booming populations of chinstrap and gentoo penguins, which can switch from eating krill to fish and squid.

''This will create an immense instability in the system with unpredictable consequences,'' Dr. Giannini said. ''And that's not good. The rat will be very happy with this change, but we don't want rats. We want penguins.''

Photo: Penguins seem to have originated in Antarctica when it was temperate and forested. Emperor penguins, above, adapted to the cold as the climate changed. (Photo by Bonne Pioche Productions/Alliance de Production Cinématographique)